A terminal in a mobile communications network transmits and receives signals by using an antenna. With development and application of technologies, antenna bandwidth of a terminal product needs to cover more bands. In addition, in order to seek an esthetic appearance, space reserved for the antenna is increasingly smaller. Obviously, a traditional passive antenna can hardly meet requirements in an application scenario, and people pay more attention to a tunable antenna that combines a passive antenna and a tunable device.
A tunable antenna based on an IFA (Inverted-F Antenna) architecture in the prior art is shown in FIG. 1. The IFA is a classic passive antenna. A single-pole and double-throw switch is serially connected to a ground point of the IFA, and an inductor or an invariable capacitor is serially connected by using the single-pole double-throw switch to implement grounding. That the IFA is grounded by using the inductor or the invariable capacitor necessarily changes an impedance property of the tunable antenna shown in FIG. 1, thereby implementing a change of an operating band. A sum of bands that can be covered in all states of the antenna is antenna bandwidth.
However, a low-frequency resonance frequency of the tunable antenna depends on a length of a long branch of an intermediate- or low-frequency radiator of radiators. A length of the radiator affects an overall size of the antenna. That is, in a case in which the size of the antenna is limited to some extent, the antenna bandwidth may be relatively narrow and cannot meet application requirements.